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Thyroxine (total T4)

SI UNITS (recommended)


* The SI units is the recommended method of reporting clinical laboratory results

Total Thyroxine, Total T4
Units of measurement
nmol/L, µg/dL, µg/100mL, µg%, ng/mL, µg/L

The hormone thyroxine (T4) is the main product secreted by the thyroid gland and is an integral component of the hypothalamus‑anterior pituitary‑thyroid regulating system. It has the function of anabolically influencing metabolism. Thyroxine is formed in a coupling reaction from two DIT molecules (3,5‑diiodotyrosine) in the thyroid gland. It is stored bound to thyroglobulin in the lumina of the thyroid follicles and is secreted as required under the influence of TSH.

The major part (> 99 %) of total thyroxine (T4) in serum is present in protein‑bound form. As the concentrations of the transport proteins in serum are subject to exogenous and endogenous effects, the status of the binding proteins must also be taken into account in the assessment of the thyroid hormone concentration in serum. If this is ignored, changes in the binding proteins (e.g. due to estrogen‑containing preparations, during pregnancy or in the presence of a nephrotic syndrome etc.) can lead to erroneous assessments of the thyroid metabolic state.

The determination of T4 can be utilized for the following indications: the detection of hyperthyroidism, the detection of primary and secondary hypothyroidism, and the monitoring of TSH‑suppression therapy.

SI units Conversion Calculator. Convert Thyroxine (total T4) level to nmol/L, µg/dL, µg/100mL, µg%, ng/mL, µg/L. Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Thyroxine (total T4) unit conversion to nmol/L, µg/dL, µg/100mL, µg%, ng/mL, µg/L.